As development of long-haul networks begins to saturate and the demand for larger bandwidth in the networks starts to expose bottlenecks at the user-end, the focus of optical network development has shifted away from long-haul networks to smaller and more dynamic networks, such as metropolitan area networks (MANs). As a result, new network design and planning rules, for example, related to the placement of network components, have to be developed.
Specifically, determining the locations and gain settings of optical amplifiers in MANs is a new design issue that has arisen since the growth in the size of MANs has reached the degree that amplification has become necessary in MANs. However, many of the current amplifier placement methods do not attempt to optimize network parameters such as cost associated with amplifiers or optical signal to noise ratio (OSNR) of signals. As well, many amplifier placement methods are specific to a particular network topology, such as star or ring topologies, and cannot be applied to the more complex mesh topology.
For example, there exist methods of determining amplifier placement that are simple and methodical, as illustrated by the following two examples.
An article by Byrav Ramamurthy, Jason Iness, and Biswanath Mukherjee published in Proceedings of IEEE INFOCOM '97, pages 261–8, 1997 and entitled “Minimizing the Number of Optical Amplifiers Needed to Support a Multi-Wavelength Optical LAN/MAN” discloses two methods of determining amplifier placement, one termed the As Soon As Possible (ASAP) method, and the other termed the As Late As Possible (ALAP) method. Amplifier placement is determined solely by power levels along optical links in the network.
An article by Chung-Sheng Li, Franklin Fuk-Kay Tong, Christos J. Georgiou, and Monsong Chen published in Proceedings of IEEE INFOCOM '94, pages 130–7, 1994 and entitled “Gain Equalization in Metropolitan and Wide Area Optical Networks Using Optical Amplifiers” discloses a method of determining amplifier placement in the network by traversing the network in an upstream direction and placing amplifiers to maintain power levels at specific locations in the network.
These two methods described above do not attempt to minimize the number of amplifiers in the network, nor do they perform an assessment of the effectiveness of particular amplifier locations for the network as a whole.
Advanced methods of determining amplifier placement in a network involve formulating a mathematical equation for the amplifier placement and solving the equation, as is illustrated by the following three methods.
An article by Byrav Ramamurthy, Jason Iness, and Biswanath Mukherjee published in Journal of Lightwave Technology, volume 16, pages 1560–9, September 1998 and entitled “Optimizing Amplifier Placements in a Multiwavelength Optical LAN/MAN: The Equally Powered-Wavelengths Case” discloses a method of determining the minimum number and locations of optical amplifiers required in a network by solving the amplifier placement equation with a mixed-integer linear program (MILP) software package. This method is applicable only to star coupler-based networks and assumes the artificial constraint that the powers on the wavelengths at any given point in the network are equal.
An article by A. Fumagalli, G. Balestra, and L. Valcarenghi published in Proceedings of the SPIE—The International Society for Optical Engineering, volume 3531, pages 268–79, 1998 and entitled “Optimal Amplifier Placement in Multi-Wavelength Optical Networks Based on Simulated Annealing” discloses a method of determining the placement of optical amplifiers required in a network by solving the amplifier placement equation with a heuristic algorithm. This method is applicable only to broadcast-and-select networks.
An article by Byrav Ramamurthy, Jason Iness, and Biswanath Mukherjee published in IEEE/ACM Transactions on Networking, pages 755–67, December 1998 and entitled “Optimizing Amplifier Placements in a Multi-Wavelength Optical LAN/MAN: The Unequally-Powered-Wavelengths Case” discloses a method of determining the minimum number and locations of optical amplifiers required in a network by solving the amplifier placement equation with a nonlinear solver. This method is applicable only to star coupler-based networks.
In the above-mentioned methods, optical amplifier placements are unrestricted so that an optical amplifier may be placed at any location along the lightpaths of the network. In practice though, optical amplifiers often have to be placed into existing optical networks, and thus there exists the added constraint that optical amplifiers may only be placed at easily accessible locations along the lightpaths of the network. The above-mentioned methods do not take such constraints into account.
Therefore, there is a need in the industry for the development of a method and system for determining the locations and gain settings of optical amplifiers in an optical network that is applicable to a variety of network topologies and takes into account additional factors and existing network limitations such as amplifier cost and location restrictions.